1. Field of the Invention
The invention relates to a spark ignition type internal combustion engine.
2. Description of the Related Art
In the related-art, there is a known spark ignition type internal combustion engine that has a variable compression ratio mechanism capable of changing the mechanical compression ratio, and a variable valve mechanism capable of changing a valve characteristic of an intake valve or an exhaust valve (e.g., Japanese Patent Application Publication No. 2001-263099 (JP-A-2001-263099)).
In the related-art variable compression ratio mechanism, the mechanical compression ratio is heightened by lessening the combustion chamber volume measured when the piston is positioned at the compression top dead center. Therefore, when the mechanical compression ratio has been heightened by the variable compression ratio mechanism, the distance between the piston and the cylinder head at the top dead center is relatively short, so that there is possibility of interference between the piston and the intake valve.
Therefore, in Japanese Patent Application Publication No. 2001-263099, when the mechanical compression ratio has been heightened, the variable valve mechanism is controlled so as to retard the valve opening timing of the intake valve or lessen the amount of lift of the intake valve. This can restrain the interference between the piston and the intake valve even when the mechanical compression ratio has been heightened.
Besides, in Japanese Patent Application Publication No. 2001-263099, the variable compression ratio mechanism and the variable valve mechanism have actuators for changing the mechanical compression ratio and the valve characteristic, respectively, and these actuators are connected, independently of each other, to an electronic control device. That is, the variable compression ratio mechanism and the variable valve mechanism are controlled independently of each other by the electronic control device.
However, in the case where the variable compression ratio mechanism and the variable valve mechanism are controlled independently of each other as mentioned above, if an abnormality occurs, for example, in a sensor that detects the amount of control of the variable valve mechanism, an undesired event can occurs, for example, an event where although the mechanical compression ratio is high, the valve opening timing of the intake valve is not retarded, so that the piston and the intake valve interfere with each other. That is, in the case where the aforementioned two mechanisms are controlled independently of each other, there is possibility of the piston and the intake valve interfering with each other if a trouble, such as a failure or the like, occurs in either one of the control systems of the two mechanisms.